1. Field of the Invention
The present invention relates generally to devices and methods for assembling permanent magnet electrical machines, and more particularly to an apparatus and method for improving focused flux configured devices.
2. General Background and State of the Art
Permanent magnets make it reasonable to build electrical machines (defined here as motors and generators) using these for field generation rather than electro-magnets. Typically the magnets are mounted on an inner rotor, but outer rotor mounting is also used. In a generator, the rotation of the magnets on the rotor generates magnetic fields that induce voltages and currents in the windings of the radial outward stator. In a motor, the magnets react to voltages and currents applied to the stator and cause rotation of the rotor.
Permanent magnet electrical machines are more compact and simpler and require less maintenance than their electromagnetic brethren by not requiring rotor electromagnet windings. Modern Rare Earth magnets provide a much denser source of powerful magnetic flux than can windings, and have high flux and are capable of withstanding reasonably high temperatures. The resulting compact machines find application in structures where size, weight and efficiency are important, such as generators within the nacelles of wind power generators located on the top of high towers, or as motors where space is a premium.
Permanent magnets are mounted to the rotor in such a manner that the generated magnetic flux interacts with the stator coils. The standard surface mount configuration is to have the magnet poles parallel and circumferential to the surface, and the focused flux configuration has the magnets mounted with their poles perpendicular and circumferential to the rotor surface. As the magnetic flux is roughly proportional to the surface area of the magnet pole, the focused flux configuration can produce higher flux levels as the radial magnet pole side area can be made larger than that of the standard configuration having the same number of stator windings. Further, surface loss self-heating of focused flux machines are far lower than surface mount machines due to the reduced exposure of the magnet poles to induced flux variations.
One of the manufacturing issues related to focused flux machines is the mounting of the magnets to the rotor in a manner that contains the centripetal forces on the magnets due to the rotor rotation in normal operation. Conventionally, focused flux magnets are mounted by bonding, banding (with a non-ferrous material such as fiberglass, carbon fiber or Kevlar tape) or gripping them to the rotor surface. A novel means to mount focused flux magnets, the subject of this invention, improves on the manufacturing issue as well as increasing cooling and making the electrical machine easier to assemble.